While GFP
as a reporter gene has mostly been used for qualitative studies,
its great potential as a quantitative, real time and on-line indicator
for protein production has been realized in recent years. Albano
et al. first demonstrated that GFP fluorescence could be used to quantitatively
monitor GFP-fusion protein production in E. coli (Albano et al., 1996;
Albano et al., 1998). Other work using GFP for monitoring and controlling
in E. coli were also successful (Poppenborg et al., 1997; Delisa et al.,
1999; Chae et al., 2000). Other than E. coli, GFP has also been used to
monitor protein production in yeast (Li et al., 2000) and insect cells
(Cha et al., 1997). Meanwhile, various methods and devices for quantitative
measurements of GFP were developed (Randers-Eichhorn et al., 1997; Craig
et al., 1997; Korf et al., 1997; Endow and Piston, 1998 and Knight et al.,
1999).